Kerberos: The Definitive Guide

The World’s Shortest ASN.1 Tutorial

ASN.1 is an acronym for Abstract Syntax Notation One. It defines a methodology for describing protocol definitions in an abstract notation, and then provides several methods to convert those abstract definitions into a stream of bytes for transmission over a communications network. Several protocols use ASN.1 to define their protocols; along with Kerberos 5, SNMP and LDAP are popular protocols that use ASN.1.

As we saw earlier with the Kerberos 4 protocol definition, extensibility is an important attribute when designing protocols. No protocol remains static; it is much more efficient for both the implementer and users if a protocol has forward and backward compatibility built in from the start. A manually designed and coded protocol design such as that in Kerberos 4 is very difficult to add onto later, unless extreme care is undertaken during the design of the initial protocol. In addition, manual coding of the network encoding and decoding modules leads to bugs that then lead to trouble with interoperability when new implementations must work around or conform to bugs in the initial implementation. ASN.1 can help with both of these problems.

ASN.1 provides a grammar with which protocol designers can describe an application’s protocol. ASN.1 also provides several built-in types such as INTEGER, representing an arbitrary integer number, and OCTET STRING, representing a string of characters. By chaining together these basic types to build more complex ...